Ann wants to choose from two telephone plans. plan a involves a fixed charge of $10 per month and call charges at $0.10 per minute. plan b involves a fixed charge of $15 per month and call charges at $0.08 per minute. which statement correctly compares the two plans? a) plan a is cheaper than plan b if the usage is less than 400 minutes. b) plan a is cheaper than plan b if the usage is less than 250 minutes. c) plan a is cheaper than plan b if the usage is more than 400 minutes. d) plan a is cheaper than plan b if the usage is more than 250 minutes.